The flight was postponed because the original April 19 date conflicts with Russia’s plans to send a cargo ship to the International Space Station.

Endeavour is now scheduled to blast off April 29 with Mark Kelly at the helm. It will be the next-to-last shuttle mission. Shuttle Atlantis will close out the 30-year shuttle program this summer.

NASA announced the postponement Monday, after conferring over the weekend with the Russian Space Agency and other space station partners.

An unmanned Russian cargo ship is set to blast off at the end of April. NASA did not want the craft docking at the space station while Endeavour was still there. Now, the cargo ship will arrive first.

NASA spokesman Allard Beutel said the Russians were reluctant to postpone the supply run because of a time-sensitive biological experiment aboard the craft.

Kelly and five crewmates will deliver a $2 billion physics experiment to the space station, as well as critical spare parts to keep the orbiting outpost running for another decade.

The two-week mission will be the last for Endeavour, the baby of NASA’s shuttle fleet. It was built to replace Challenger, which was destroyed during liftoff in 1986.

The postponement puts the launch, scheduled for 3:47 p.m., on the same day as the wedding of Britain’s Prince William and Kate Middleton.

Endeavour is checking out fine at the launch pad following last week’s severe storms that brought high wind, lightning strikes, hail and even funnel clouds to Kennedy Space Center. Only inconsequential damage was found on the insulating foam of Endeavour’s external fuel tank, officials said.

Kelly returned to training in February after taking time off to be at his wife’s hospital bedside. Giffords was shot in the head in Tucson, Ariz., in early January. She is recuperating in Houston, home to Kelly and the rest of NASA’s astronaut corps. Kelly said last week that he’s awaiting doctors’ final approval for his wife to attend his launch.

In Kazakhstan, meanwhile, two Russians and an American blasted off from Kazakhstan early Tuesday for a trip to the space station. They will join three astronauts already in orbit.